With the proliferation of cellular phones, there has been pressure to improve the battery power capability to supply these devices. The efficacy of these phones relies on mobility and such mobility requires efficient battery power. From the start the batteries used have been rechargeable, prompting significant development in the structure of rechargeable batteries. Under normal conditions, the charging of such batteries is accomplished by circuitry built into the control microprocessor of the cellular phone. In order to operate, however, the controller requires a minimum voltage level from the batteries. A problem therefore arises when the battery charge is depleted below these minimum levels.
It is a purpose of this invention to provide an improved charging system for depleted batteries.
One of the prior art solutions to this charging problem is shown schematically in FIG. 1. In this instance, a start up module is added to the controller circuit to provide a limited initial constant current charge at a low current for example from 100 ma to 180 ma. This charging current is allowed to build the battery voltage to a level which will support the operation of the main controller. The controller will then take over, switching off the start-up charging module and allowing the battery to charge in a more rapid conventional manner.
In the start up mode at which the controller 2 is disabled, the start up current must be limited in order avoid excessive power loss. The power loss is caused by the need to dissipate the voltage drop from the charger voltage to the battery voltage. In view of the limited charge current, the start up mode requires an unacceptably long period of time to reach the operative voltage of the controller 2.
It is a purpose of this invention to provide a quicker start up charging mechanism which operates with lower power consumption.